Visible light that is ordinarily used to illuminate an area can be used for data communication purposes. For example, visible light from a lighting fixture can be used to simultaneously illuminate an area as well as communicate with other devices such as other lighting fixtures. To illustrate, one or more light sources (e.g., light emitting diodes (LEDs)) of a lighting fixture can be turned on and off at a relatively high frequency/rate such that the switching of the emitted light is undetectable by people while the on-off switching can be detected by a receiving device. Similarly, the intensity level of the emitted light can be changed at a high enough frequency/rate such that the resulting cycling of the light is not detectable by people. However, cycling of the emitted light that is undetectable by people can be used to represent data intended for a receiving device that is capable of detecting the cycling.
In some applications, a lighting fixture may be turned on or off based on the detection of motion. For example, an occupancy detector (e.g., infrared motion detector) associated with a lighting fixture may be used to detect motion in a monitored area. The lighting fixture can be turned on or off based on an output signal from the occupancy detector that indicates whether a motion is detected. In some applications, an active device that transmits an output signal may be used for occupancy detection. For example, the device may rely on detecting Doppler shifts to detect motion in the monitored area. U.S. Pat. No. 8,232,909, issued to the assignee of this patent application and incorporated herein by reference, describes a device that relies on Doppler shift to detect motion.
In some applications, a device (e.g., a lighting fixture) that uses visible light to illuminate an area, communicate with other devices and detect motion may eliminate the need for a separate occupancy detector.